Plusses and minuses of each. I am told that lexan might be a better replacement than plexiglass. Lexan wont break etc. However I have never seen a "broken" front or back window on a scamp plus I am installing a gravel guard.

Thoughts?

From what I have read:
Plexiglass:
cheaper
scratches - can be restored by sanding and buffing
resistant to breaking - when breaks pieces are large and dull edged

Polycarbonate:
15% more expensive
untreated sheet discolors in 5-7 years of sun exposure
scratches - cannot be restored by sanding and buffing

Also I have been quoted 350-400 for two cut windows installed, maybe 300 for installed plexiglass is the cheapest option. Does this sound about right or shall I keep shopping around??

Ive looked for other threads comparing, but didnt find it so donna if you know of an existing thread, point me there please.

You are correct in those general comments. Poly also has a much greater impact resustance but is also more flexible. I personally installed Poly in my Boler.
You can do the windows yourself, here is everything you need to know.Front & Rear Windows

Poly/Lexan is much easier to cut at home. Cuts well with a sabre or band saw. Plexi just melts and fuses back together. I believe both cut by scoring deeply and snapping, though that can be tricky, especially curved cuts.

I cut Lexan by scoring/snapping with no problem, but they were straight cuts. I took a stained glass class, and it was the same method but even a little easier. If I had to do curves,which were a little trickier, for me, I'd just call around to stained glass artists' shops and sweetly ask for someone to do the cuts. They'd do it a lot cheaper, than a window place, I think. Maybe even free if you sound pitiful enough...

Lexan/Poly is what covers headlights & tail lights on vehicles. Cuts fine on a table saw with an 80 tooth or finer carbide blade, also easily shaped with a router if you make a template to follow for your window shape. Edges smooth well with medium sandpapers. I use it in 1/8th to 3/16 thicknesses.

Plexiglass doesn't hold up well to road grit and ANY abrasives when you wash the trailer.